Memory exhaustion via sparse high-offset STREAM frames
Published Jul 16, 2026 · Updated Jul 16, 2026
Uncontrolled resource consumption in H2O quicly before commit 8b178e6 allows remote attackers to exhaust memory via sparse STREAM frames. Connection-level credit uses each stream’s largest received offset instead of bytes removed from receive buffers, so a one-byte frame at the permitted maximum unlocks more credit while a buffering application reserves the intervening range. Exposure requires a QUIC peer and an application that buffers out-of-order data; default H2O settings raise the per-connection memory ceiling by about fourfold.
Summary
What happened
Uncontrolled resource consumption in H2O quicly before commit 8b178e6 allows remote attackers to exhaust memory via sparse STREAM frames. Connection-level credit uses each stream’s largest received offset instead of bytes removed from receive buffers, so a one-byte frame at the permitted maximum unlocks more credit while a buffering application reserves the intervening range. Exposure requires a QUIC peer and an application that buffers out-of-order data; default H2O settings raise the per-connection memory ceiling by about fourfold.
The record
- CVE
- CVE-2026-44433
- Published
- Jul 16, 2026
- Updated
- Jul 16, 2026
- Vendor
- H2O Project
- Product
- quicly
- Classifications
- CWE-770, CWE-400, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 16, 2026CVE publishedPublication date reported by the CVE source.
- Jul 16, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=< 8b178e6
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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